The field of application of the invention is satellite antennas, radar antennas, aircraft antennas, generally ground-based or on-board antennas integrating networks of radiating elements.
In emission, the radiating elements of the network antenna are fed with electromagnetic signals which are digitally phase-and-amplitude-weighted beforehand with excitation coefficients determined by computing means. In reception, the electromagnetic signals received by elements of the network antenna are then phase-and amplitude-weighted digitally with excitation coefficients determined by these same computing means. These excitation coefficients are used in reception for transforming the signals received by the elements of the network antenna and stemming from one or several directions into a useful coherent signal, and in emission for transforming a useful signal into different signals feeding the elements of the network and forming one or more given illumination beams, in both cases for observing a certain intended illumination law for the network. One skilled in the art will recognize in the digital generation of the excitation coefficients and in the digital weighting of the signals of the elements of the network antenna, a digital network for forming beams (Digital Beamforming Network or DBFN).
One of the problems of large size network antennas is the fact that the arrangement and the orientation of the elements of the network may vary over time.
For example, an orbiting satellite may be subject to sudden changes in temperature according to whether it is illuminated by the sun or not.
The result is deformations of the antenna due to the existence of significant thermal gradients.
Generally, the antenna may be subject to significant thermal and mechanical stresses generating deformations of the latter.
These deformations perturb the illumination law of the elements of the network.
Presently, in order to limit these deformations, it is resorted to mechanical structures supporting the network antenna, the design of which should allow the rigidity, the flatness and the shape of the antenna to be maintained under very severe thermal and mechanical stresses. Consequently, these mechanical supporting structures generally have significant mass, cost and bulkiness.
Presently, the functions for calibrating the elements of the network are generally ensured by using couplers inserted in the emission circuit in order to pick up a portion of the signal sent to the emitting elements.
Another calibration solution consists of conducting remote measurements. For example, on an orbiting satellite, the measurements are carried out from an earth station.
These means are burdensome and costly to apply and the corrections cannot always be made in real time for reasons of logistics and/or cost-effectiveness. Further, many approximations are made during these measurements (mutual couplings between elements not taken into account, behavior of the radiating elements not taken into account, non-exhaustive tests, etc.) This is detrimental to optimum operation of the antennas since the environmental conditions under which the latter are found (high and rapid temperature gradients for example for space antennas, winds for radar, ground antennas, etc.) cause variations in the shape of the network, in the performances of the radiating elements and in the resulting radiation diagram of the antenna. The consequences are designs of antennas with complex and often heavy and bulky mechanical structures.